A control circuit may drive a power device such as a motor by delivering control signals to a power conversion circuit. In a technique known as trapezoidal control, the back electromagnetic force (EMF) has a trapezoidal shape. The torque on the power device that results from trapezoidal control includes a ripple that can decrease the efficiency of the power device. Moreover, trapezoidal control can also cause audible noise at the power device.
Another technique for controlling a power device is called sinusoidal control, where the control circuit may cause a gate driver circuit to deliver pulse-modulated signals, such as pulse-width modulation signals (PWM) or pulse-frequency modulation signals, to a power conversion circuit. By varying the duty cycle, frequency, and/or phase of the pulse-modulated signals, the control circuit may cause the power conversion circuit to deliver electrical currents to the power device with a sinusoidal waveform. The power conversion circuit may drive the electrical currents through windings, causing the windings in the power device to create magnetic fields that vary over time. Ideally, the interaction between the varying magnetic fields and the magnets in a rotor of the power device should result in a torque to drive the power device, where the torque is proportional to the electrical currents through the windings.
One example sinusoidal control technique is V/Hz or V/f control, which includes algorithms to control motor speed based on the voltage applied to the windings. For V/Hz control, the speed of the rotor may increase with increasing voltage.
Sinusoidal control can provide better acoustic performance, which is more suitable for applications like refrigerator fans, HVAC (heating, ventilation, and air conditioning) fans, pumps, and other home appliances. Trapezoidal control can provide higher driving torque, which is more suitable for systems with heavy and unpredictable load conditions, such as power tools and actuators. However, implementing sinusoidal commutation normally requires digital signal processing or micro-controllers with high-frequency PWM modulators to achieve the desired resolution in time and generate the sinusoidal waveform.